A QCD analysis of \bar p N -> gamma^* pi and \bar p N -> gamma^* gamma. Where is the pion in the proton ?

Abstract

We study the scaling regime of nucleon-anti-nucleon annihilation into a deeply virtual photon and a photon or meson, \bar p N -> gamma ^* pi, \bar p N -> gamma ^* gamma, in the forward direction. The leading twist amplitude factorizes into an antiproton distribution amplitude, a short-distance matrix element and a long-distance dominated transition distribution amplitude (TDA) which describes the nucleon to meson or photon transition. The impact representation of this TDA maps out the transverse locations of the small size core and the meson or photon cloud inside the proton.